Product name: Acrylic acid
CAS number: 79-10-7
Molecular formula: C3H4O2
EINECS number: 201-177-9

Overview

Acrylic acid is the simplest unsaturated carboxylic acid, with a molecular structure consisting of a vinyl group and a carboxyl group. Pure acrylic acid is a colorless, clear liquid with a characteristic pungent odor. Density 1.0511. Melting point 14°C. Boiling point 140.9°C. Strong acidity. Corrosive. Soluble in water, ethanol and ether. Active chemical properties. Easy to polymerize into a transparent white powder. Propionic acid is generated when reduced. 2-chloropropionic acid is generated when hydrochloric acid is added, which is used to prepare acrylic resins, etc., and is also used in other organic syntheses. It is obtained by oxidation of acrolein or hydrolysis of acrylonitrile, and can also be synthesized from acetylene, carbon monoxide and water, or by pressurized oxidation of ethylene and carbon monoxide.

Chemical reactions

Acrylic acid can undergo characteristic reactions of carboxylic acids, and can also react with alcohols to give corresponding esters. The most common acrylates include methyl acrylate, butyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate. Acrylic acid and its esters can undergo polymerization reactions to form homopolymers or copolymers by themselves or when mixed with other monomers. Monomers that can usually copolymerize with acrylic acid include amides, acrylonitrile, vinyl-containing monomers, styrene, and butadiene. These polymers can be used to produce a variety of plastics, coatings, adhesives, elastomers, floor polishes, and paints.

Chemical properties

Colorless liquid with pungent odor. Soluble in water, ethanol and ether.

Acrylic resin

Acrylic resin is a general term for resins formed by polymerization of acrylic acid and methacrylic acid or their derivatives such as esters, nitriles, and amides. It is a colorless and transparent resin with a specific gravity between 1.17 and 1.20. It has high transparency, a light transmittance of 92% to 98%, and a refractive index of 1.48 to 1.50. Its excellent optical properties are comparable to those of optical glass. It can transmit ultraviolet rays, so it is commonly known as organic glass. It is light-resistant, aging-resistant, and easy to color. It can be colored in various bright colors. Even if it is heated and bent at a temperature of 95℃ to 110℃, it will not produce whitening and cracking. It is light and not easy to break, and can be used as a substitute for glass. It has good processing performance, and the molded products can be bent, bonded, and machined for secondary processing. Because of this good property, the resin is often used in optical lenses, lenses, etc., such as Schmidt lenses and Fresnel lenses for televisions, goggles, art supplies, and furniture. Acrylic resins are available in solids, solutions, and dispersions. It is widely used as lighting materials, decorations, advertising nameplates, coatings, etc. Its wider application is limited by its high cost. If methyl groups are replaced by cyano groups for polymerization, it can become an instant adhesive, which is often used for bonding glass, metal, plastic, rubber, etc.

Acrylic paint

Acrylic paint mainly includes thermoplastic acrylic paint, thermosetting acrylic paint, high-solid acrylic paint, acrylic ester latex paint, and water-diluted acrylic resin paint.
(1) The main component of thermoplastic acrylic paint is polymethyl methacrylate, but pure polymethyl methacrylate is too brittle and has poor adhesion to the substrate. The solvent is not easy to fully utilize because of its high glass transition temperature. The solid content of solvent-based thermoplastic acrylic paint is too low (volume concentration is about 12%). After entering the 1970s, the usage dropped sharply. Thermosetting acrylic paint has been developed instead, and high-solid acrylic paint is particularly promising.
(2) Thermosetting acrylic resin can increase the non-volatile content of the paint. After the paint is applied, cross-linking occurs during the curing process. In addition to having a higher solid content, thermosetting acrylic paint also has better gloss and appearance, better chemical resistance, solvent resistance, alkali resistance, and heat resistance. The disadvantage is that it cannot be stored for a long time. Thermosetting acrylic paint uses melamine-formaldehyde resin or polyisocyanate as a cross-linking agent.
(3) It is difficult to prepare acrylic resin for high-solids coatings. Generally, the volume solid content of high-solids polyester coatings can reach 65% to 70%. Polyester can easily ensure that there are more than two hydroxyl groups on each molecule, but it is difficult for acrylic resin to achieve more than two hydroxyl groups on each molecule. To solve this problem, one is to increase the amount of hydroxyethyl methacrylate (HEMA), such as increasing it to 15%; the other is to make the molecular weight distribution of the resin as narrow as possible and the distribution of polar groups as uniform as possible. The latter is very critical in high-solids coatings. At present, the volume solid content of high-solids acrylic resin coatings at spraying viscosity can reach 54% to 56% (weight solid content can reach 70% to 72%).
(4) Acrylic latex is the best and most important latex. Compared with polyvinyl acetate emulsion, acrylic emulsion improves the flexibility and adhesion of the coating and has moderate cost. In addition, its outdoor durability, including resistance to UV degradation, is significantly improved, so it has been used in wall architectural coatings, scrubbable and decontaminated floor varnishes, and paint printing pastes.
(5) Water-dilutable acrylic resins are thermosetting resins that are first prepared as water-soluble polymers, which are then cross-linked into a water-resistant and tough coating during film formation. Water-dilutable acrylic coatings can be used for spray painting, dip painting, and other applications. The most successful application is can lining coatings. Another important application is electrophoretic paint.

Chemical properties

Uses

Preparation of polymers through homopolymerization or copolymerization, used in coatings, adhesives, solid resins, molding compounds, etc.

Uses

Acrylic acid and its series of products, mainly its esters, have developed rapidly in recent years. Like ethylene, propylene, vinyl chloride, acrylonitrile, etc., they have developed into important raw materials for the polymer chemical industry. As monomers of polymer compounds, the total global output of acrylic acid and its esters has exceeded one million tons, and the output of polymers and copolymers (mainly emulsion resins) made from them is nearly 5 million tons. These resins are used in many sectors such as coatings, plastics, textiles, leather, papermaking, building materials, and packaging materials. Acrylic acid and its esters can be used for organic synthesis and polymer synthesis, and most of them are used in the latter, and more often they are copolymerized with other monomers such as vinyl acetate, styrene, methyl methacrylate, etc. to produce synthetic resins with various properties, functional polymer materials and various additives.
Main application areas:
(1) Warp sizing material Warp sizing material prepared from raw materials such as acrylic acid, methyl acrylate, ethyl acrylate, acrylonitrile, ammonium polyacrylate, etc. has a lower capacity desizing than polyvinyl alcohol sizing material and saves starch. (2) Adhesives use copolymer latexes such as acrylic acid, methyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate, which can be used as adhesives for electrostatic flocking and flocking, and have good fastness and feel.
(3) Water thickeners use copolymers of acrylic acid and ethyl acrylate to make high molecular weight powders. They can be used as thickeners and used in oil fields. Each ton of product can increase crude oil production by 500 tons, and have a good effect on oil production in old wells.
(4) Coated paper finishing agents use quaternary copolymer latexes such as acrylic acid, butyl acrylate, 2-ethylhexyl acrylate, and styrene as coated paper coatings. They retain color and do not turn yellow. They have good printing performance and do not stick to rollers. They are better than styrene-butadiene latex and can save dry coolants.
(5) Polyacrylates can use acrylic acid to produce various polyacrylate products (such as ammonium salts, sodium salts, potassium salts, aluminum salts, nickel salts, etc.). They are used as coagulants, water treatment agents, dispersants, thickeners, food preservatives, acid- and alkali-resistant desiccants, softeners, and other polymer additives.

Production methods

1. Cyanoethanol method This method uses chloroethanol and sodium cyanide as raw materials to react to produce cyanoethanol. Cyanoethanol is hydrolyzed at 175°C in the presence of sulfuric acid to produce acrylic acid: if the hydrolysis reaction is carried out in methanol, methyl acrylate is produced.

2. Acrylonitrile hydrolysis method Acrylonitrile is first hydrolyzed with sulfuric acid to produce acrylamide sulfate, and then hydrolyzed to produce acrylic acid, with ammonium bisulfate as a by-product. This method has been greatly developed by Rohm-Haas Company in the United States.

3. High-pressure Repe method Acetylene dissolved in tetrahydrofuran is reacted with carbon monoxide and water in the presence of a catalyst composed of nickel bromide and copper bromide to produce acrylic acid. The characteristics of this method are: using tetrahydrofuran as a solvent can reduce the danger of high-pressure treatment of acetylene; at the same time, the catalyst does not need to use carbonyl nickel used in the original Repe method, but only nickel salt. Propylene is mixed with air and water vapor in a certain molar ratio, and in the presence of a composite catalyst such as molybdenum-bismuth, the reaction temperature is 310-470°C, and acrolein is oxidized at normal pressure to produce acrolein with a yield of 90%. Then, acrolein is mixed with air and water vapor in a certain molar ratio, and in the presence of a composite catalyst such as molybdenum-vanadium, the reaction temperature is 300-470℃, and the oxidation is carried out at normal pressure to obtain acrylic acid, with a yield of up to 98%. This method is divided into one-step and two-step methods. The one-step method is that propylene is oxidized in one reactor to produce acrylic acid; the two-step method is that propylene is first oxidized in the first reactor to produce acrolein, and the acrolein then enters the second reactor for oxidation to produce acrylic acid. The two-step method is divided into fixed bed and fluidized bed methods according to the reactor structure. Among the industrial production methods of acrylic acid, the cyanoethanol method and the high-pressure Repe method have been basically eliminated. The previously used acetic acid as a raw material is cracked into ethylene ketone, and then reacted with anhydrous formaldehyde to produce propiolactone, and then isomerized with hot phosphoric acid to acrylic acid. The so-called ene ketone method or β-propiolactone method is also basically eliminated, and only a few old devices use the acrylonitrile method. At present, the main methods used in industry are the improved Repe method and propylene oxidation method, and the latter is more common and has the most development prospects. In the patent report, there is also a production method using propionic acid as a raw material.

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